Antonio Ancona

Analytical characterization of laser-generated copper nanoparticles for antibacterial composite food packaging

AbstractA new type of nanomaterial has been developed as antibacterial additive for food packaging applications. This nanocomposite is composed of copper nanoparticles embedded in polylactic acid, combining the antibacterial properties of copper nanoparticles with the biodegradability of the polymer matrix. Metal nanoparticles have been synthesised by means of laser ablation, a rising and easy route to prepare nanostructures without any capping agent in a liquid environment. As prepared, nanoparticle suspensions have been easily mixed to a polymer solution. The resulting hybrid solutions have been deposited by drop casting, thus obtaining self-standing antibacterial packages. All samples have been characterized by UV–Vis spectroscopy, X-ray photoelectron spectroscopy and electro-thermal atomic absorption spectroscopy. Ion release data have been matched with bioactivity tests performed by Japanese Industrial Standard (JIS) method (JIS Z 2801:2000) against Pseudomonas spp., a very common Gram-negative microbial group able to proliferate in processed food.n Online abstract figureAnalytical characterization of copper nanoparticles: an XPS spectrum and a TEM image

Friction Properties of Lubricated Laser-MicroTextured-Surfaces: An Experimental Study from Boundary- to Hydrodynamic-Lubrication

We present measurements of friction coefficient of lubricated laser surface textured (LST) microstructures with two different geometries. The former is made of a square lattice of microholes; the latter is constituted by a series of microgrooves. We analyze sliding velocities spanning more than two orders of magnitude to cover the entire range from the boundary to the hydrodynamic regime. In all cases, the interfacial pressure is limited to values (relevant to particular manufacturing processes) which allow to neglect macroscopic elastic deformations, piezo-viscosity and oil compressibility effects. The measured Stribeck curves data are compared with those obtained for the flat control surface and show that the regular array of microholes allows to reduce friction over the entire range of lubrication regimes with a decrease of about 50xa0% in the hydrodynamic regime. On the contrary, the parallel microgrooves lead to an increase of friction compared to the flat control surface with a maximum increase of about 80–100xa0% in the mixed lubrication regime. These remarkably opposite friction results are then explained with the aid of numerical simulations. Our findings confirm that LST may have cutting edge applications in engineering, not only in classical applications (e.g., to reduce piston-ring friction losses in internal combustion engines) but also, in particular, in technological processes, such as hydroforming, superplastic forming, where the mapping of the frictional properties of the mold has a crucial role in determining the final properties of the mechanical component.

A Real-Time Spectroscopic Sensor for Monitoring Laser Welding Processes

In this paper we report on the development of a sensor for real time monitoring of laser welding processes based on spectroscopic techniques. The system is based on the acquisition of the optical spectra emitted from the laser generated plasma plume and their use to implement an on-line algorithm for both the calculation of the plasma electron temperature and the analysis of the correlations between selected spectral lines. The sensor has been patented and it is currently available on the market.

Real-time in-situ measurement of the penetration depth in short pulse laser percussion drilling of metal targets

High-energy ultra-short pulse laser ablation is a fast-growing technology in precision laser micromachining of transparent as well as opaque materials. Accurate in-situ measurements of physical parameters such as the penetration depth and the removal rate are crucial to fully characterize the ultrafast laser-material interactions [1–5]. Nonetheless, the laser drilling is still lacking of a real-time technique able to monitor and control the spatial- and time-dependent evolution of the hole-depth in metallic plates.

Laser self-mixing sensor to monitor in-situ the penetration depth during short pulse laser drilling of metal targets

Direct real-time measurements of the penetration depth during laser micromachining has been demonstrated by developing a novel ablation sensor based on laser diode feedback interferometry. Percussion drilling experiments have been performed by focusing a 120-ps pulsed fiber laser onto metallic targets with different thermal conductivity. In-situ monitoring of the material removal rate was achieved by coaxially aligning the beam probe with the ablating laser. The displacement of the ablation front was revealed with sub-micrometric resolution by analyzing the sawtooth-like induced modulation of the interferometric signal out of the detector system.

Direct in-situ measurement of the ablation rate in short pulse laser percussion drilling of metal targets

We demonstrate that a non-invasive sensing technique based on optical feedback interferometry is capable to instantaneously measure the ablation front displacement and the removal rate during ultrafast laser percussion drilling of metallic plates. The sawtooth-like modulation of the interferometric signal out of the detecting sensor has been analyzed to reveal the time dependence of the removal depth with sub-micrometric resolution. Various dynamic factors related to the influence of laser pulse duration and peak energy have been assessed by in-situ spatial- and time-dependent characterization all through the ablation process. The importance of real-time measurement of the ablation rate is crucial to improve the basic understanding of ultrafast laser-material interactions. Moreover, the detection system results high-sensitive, compact, and easily integrable in most industrial workstations, enabling the development of on-line control to improve the ablation efficiency and the quality of laser micro-machining processes.We demonstrate that a non-invasive sensing technique based on optical feedback interferometry is capable to instantaneously measure the ablation front displacement and the removal rate during ultrafast laser percussion drilling of metallic plates. The sawtooth-like modulation of the interferometric signal out of the detecting sensor has been analyzed to reveal the time dependence of the removal depth with sub-micrometric resolution. Various dynamic factors related to the influence of laser pulse duration and peak energy have been assessed by in-situ spatial- and time-dependent characterization all through the ablation process. The importance of real-time measurement of the ablation rate is crucial to improve the basic understanding of ultrafast laser-material interactions. Moreover, the detection system results high-sensitive, compact, and easily integrable in most industrial workstations, enabling the development of on-line control to improve the ablation efficiency and the quality of laser micro-machini...

Closed loop control of laser welding using an optical spectroscopic sensor for Nd:YAG and CO2 lasers

Recent developments in laser joining show the applicability of spectral analysis of the plasma plume emission to monitor and control the quality of weld. The analysis of the complete spectra makes it possible to measure specific emission lines which reveal information about the welding process. The subsequent estimation of the electron temperature can be correlated with the quality of the corresponding weld seam. A typical quality parameter, for laser welds of stainless steel, is the achieved penetration depth of the weld. Furthermore adequate gas shielding of the welds has to be provided to avoid seam oxidation. In this paper monitoring and real-time control of the penetration depth during laser welding is demonstrated. Optical emissions in the range of 400nm and 560nm are collected by a fast spectrometer. The sensor data are used to determinethe weld quality of overlap welds in AISI 304 stainless steel sheets performed both with CW Nd:YAG and CO2 lasers. A PI-controller adjusts the laser power aiming at a constant penetration. Optical inspection of the weld surface and microscopic analysis of weld cross sections were used to verify the results obtained with the proposed closed-loop system of spectroscopic sensor and controller.